In a known semiconductor package, an insulating sheet adhered to a copper foil of the same shape is attached to a lower surface of a die pad of a lead frame, on which a power MOSFET (metal oxide semiconductor field-effect transistor) is mounted.
In this semiconductor package, the lead frame, the power MOSFET, the insulating sheet and the copper foil are molded all together to obtain insulation properties and high heat radiation properties (e.g., see JP-B-3740116).
Also, in a known semiconductor package incorporating a power MOSFET and a control circuit, an insulating resin sheet is attached to and molded onto a lower surface of a die pad of a lead frame, on which the power MOSFET is mounted, to form a mixed layer of the resin sheet and a mold resin (e.g., see JP-B-4146785).
In a known method of manufacturing a semiconductor package, a press pin is used to press a die pad against an insulating sheet, followed by molding (e.g., see JP-B-3854957).
Also, in a known method of manufacturing a semiconductor package, a resin sheet is prepared, which is solid at normal temperature, and temporarily melted at high temperature but then completely cured.
In this method, a mold having temperature higher than the melting temperature of the resin sheet is also prepared.
Then, the resin is superheated and filled in the mold with the application of pressure to thermoset the resin sheet (e.g., see JP-A-2008-004971).
Further, a known semiconductor power module includes a heat sink provided with a resin sheet, and a lead frame having a bent portion of the same shape as that of the resin sheet (e.g., see JP-B-3846699).
Regarding the semiconductor package disclosed in JP-B-3740116, the small clearance between the metal and the mold resin raises a problem of low reliability under the condition where the semiconductor package has got wet.
Furthermore, this semiconductor package needs a large insulating sheet when a heat sink is made large in order to increase an area contacting the outside, and thus raises a problem of increasing cost.
Regarding the semiconductor package disclosed in JP-B-4146785, the control circuit is not in contact with the resin sheet and thus the temperature of the power MOSFET is unlikely to be transferred to the control circuit.
Due to the protective measure against the transfer of temperature from the power MOSFET, this semiconductor package has suffered from a problem of difficulty in sensing the temperature of the power MOSFET.
Furthermore, in this semiconductor package, a portion of the resin sheet tends to be melted, which portion is located near the boundary between the resin sheet and the mold resin.
As a result, the thickness of the resin sheet is reduced and thus the heat conductivity is lowered, leading to a problem of deteriorating cooling performance.
Regarding the method of manufacturing a semiconductor package disclosed in JP-B-3854957, the mold is required to have a press-pin structure, which raises a problem of making the manufacturing steps complicated.
In addition, each die pad in this method is required to have a pin-holding portion which allows the individual die pads to be closely located, raising a problem of deteriorating the insulation properties between the terminals.
Further, due to the provision of the pin-holding portion, the area of a die pad mounted with no element is increased, which raises a problem of increasing the size of the semiconductor package.
Regarding the method of manufacturing a semiconductor package disclosed in JP-A-2008-004971, the positioning of the resin sheet with respect to the mold is difficult.
In order to achieve good positioning, the resin sheet is required to be expanded over the entire bottom surface of the mold, or the mold is required to be provided with a positioning projection.
Further, the lead frames are likely to be pushed and displaced when a mold resin is filled in. Thus, this method of manufacturing a semiconductor package has suffered from a problem of low processability.
Regarding the semiconductor power module disclosed in JP-B-3846699, since the adhesion layer is stacked on the insulating layer, heat conductivity is problematically lowered to deteriorate cooling performance.
In addition, the number of processes will be increased, in this semiconductor power module, with the increase of the number of parts, which raises a problem of deteriorating processability.